1. Technical Field of the Invention
This invention relates to the medical classification of human tissue as healthy or unhealthy. More specifically, the invention uses ultrasound for determining histological characteristics of tissue by converting the return energy pulses into numerical terms, thus facilitating a quantitative analysis for medical diagnosis.
2. Discussion of the Related Art
Ultrasound has routinely been used in the medical profession to determine the shape, size and thickness of human tissue. Historically, this has been achieved through he detection of specular reflections from macroscopic tissue interfaces. Although this method allows for a general characterization of the tissue, it does not reveal its underlying health and structure. In order to obtain such a detailed analysis, reflections from the microscopic interfaces (scatterers) contained within the tissue must also be detected. An improved invention to detect these scatterers has yet to be discovered.
The prior art is able to determine general characteristics of tissue from its macroscopic interface reflections. This is commonly determined by transforming analog ultrasonic radio frequency data into a visual display. This technique requires the expertise of a skilled operator to interpret the display which does not include an accurate determination of the underlying pathology of the tissue.
Other prior art systems use Fourier Transforms to detect microscopic reflections; however, these systems do not allow for direct measurement of reflectance through self-calibration, and therefore are subject to calibration problems. These methods separate the components of an ultrasonic pulse into corresponding frequencies, using the Fourier Transform. This requires a reference plate to normalize the Fourier energy from the reflected tissue and thus the accuracy and range of available data is limited.
Similarly, the prior art taught by Sommer, Joynt, Carroll and Macovski ("Ultrasound characterization of abdominal tissues via digital analysis of backscattered wavefronts", Radiology, 141:811-7, 1981) uses a Fourier analysis to determine the mean spacing of scatterers in the liver and spleen. This method, however, does not provide for the determination of key variables that give ranges for specific tissues and their state of health.
U.S. Pat. No. 5,417,215 of Evans et al. provides a method of interpreting the microscopic interfaces which requires demodulating the return energy pulses by full-wave rectification to obtain the amplitude modulation of the pulses and computing the power spectrum by performing a Fast Fourier Transform on the rectified, digitized pulses. The requirement of rectification limits this method in providing information from the ultrasonic scan. It does not provide specific, well established physical parameters of the body tissue under investigation. It requires the comparison of Fourier energies or ratios, as well as, comparisons based on correlations.
It is, therefore, an objective of the invention to provide an improved ultrasound tissue characterization system for histological tissue classification.
It is a further objective of the invention to provide a system which does not require rectification, thereby allowing a more detailed analysis.